The EVOH is excellent in gas barrier property and transparency and, therefore, is mainly used for a food packaging material. The food packaging material is recently required to be safe particularly for food contained in a package made of the food packaging material. Further, the food packaging material preferably ensures the visibility of the contained food (preferably has higher transparency) so that the contained food can be seen through the food packaging material from the outside.
A sheet, a film or a container as the packaging material may be formed from the EVOH alone. However, it is a general practice to form a multilayer structure including an EVOH layer by stacking a layer of a thermoplastic resin other than the EVOH (other thermoplastic resin) on the EVOH layer with the intervention of an adhesive resin layer in order to impart the packaging material with higher water resistance, higher strength and other functions.
Where the packaging material including the EVOH layer and the thermoplastic resin layer is heat-drawn into a film, a sheet or a container, however, the packaging material is problematically liable to have poor appearance because the EVOH is less stretchable than the other thermoplastic resin. Therefore, it is necessary to improve the stretchability of the EVOH so that the EVOH can follow the stretching of the other thermoplastic resin.
In general, the stretchability of the EVOH tends to be improved as the content of an ethylene structural unit (hereinafter referred to simply as “ethylene content”) increases. On the other hand, the gas barrier property of the EVOH tends to be deteriorated as the ethylene content increases. Therefore, it is proposed to use an EVOH having a lower ethylene content and an EVOH having a higher ethylene content in combination to impart the EVOH with both the gas barrier property and the stretchability.
PTL 1, for example, discloses an EVOH composition containing two types of EVOHs having ethylene contents different from each other by 3 to 20 mol % and having a predetermined boron concentration. Further, PTL 1 states that a multilayer film including an intermediate layer made of the EVOH composition and a polypropylene layer provided on the intermediate layer with the intervention of an adhesive resin layer is free from stretching unevenness such as whitening and streaking even if being heat-drawn.